Irene roars into life; may become the season's first hurricane

By: Dr. Jeff Masters , 12:03 AM GMT on August 21, 2011

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Tropical Storm Irene roared into life this evening, transitioning from a tropical wave to a 50 mph tropical storm in just a few short hours. An Air Force hurricane hunter aircraft in the storm was finishing up its mission when it suddenly came across a region with intense thunderstorms and surface winds of 50 mph. The aircraft found that a center of circulation had barely closed off on the southwest edge of this region, though the plane found almost no winds from the west around the circulation center. The 6:10pm EDT center fix found a central pressure of 1007mb, which is quite high for the observed 50 mph winds. Dry air to the north and west is slowing development, as well as moderate wind shear of 10 - 20 knots, as analyzed by the University of Wisconsin CIMSS group. Infrared satellite loops and radar out of Martinique show the storm is poorly organized, with no evidence of spiral bands. The center of Irene is expected to cross over the Caribbean island of Dominica early Sunday morning, but the heaviest thunderstorms lie to the north of the center, and will affect Guadeloupe, Antigua, and St. Kitts and Nevis.


Figure 1. Evening satellite image of Irene.

The computer models have shifted southwards since yesterday, and now take Irene south of Puerto Rico on Monday, and along the south shore of the Dominican Republic on Tuesday. On Wednesday, Irene should pass near or over southern Haiti, Eastern Cuba, and Jamaica. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn Irene to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when Irene will turn to the north. We can expect that Irene will impact Central Cuba, the Bahamas, and the Florida Keys on Thursday, but it is uncertain whether Irene's turn to the north will take the storm into the Gulf of Mexico or not. Irene most reminds me of Tropical Storm Fay of 2008. Fay formed just off the coast of Puerto Rico, and was never quite able to get organized enough to become a hurricane, due to passage over Hispaniola and Cuba. Fay topped out as a strong tropical storm with 70 mph winds, and did over $500 million in damage in the U.S., mostly due to flooding rains in Florida that accumulated to over 25 inches in a few areas. Fay also dumped heavy rains on Hispaniola, triggering flooding that claimed eight lives.


Figure 2. Track of Tropical Storm Fay of 2008.

Irene will be battling dry air and moderate wind shear of 10 - 20 knots through Sunday, and it will take the storm 1 - 3 days to build up an eyewall and intensify into a hurricane. Irene is more of a threat than Tropical Storm Emily of early August was, since Irene has closed off a center farther east than Emily did and has more time to organize before encountering Hispaniola. I don't think passage over Hispaniola will destroy Irene, since it is a fairly large storm, and is likely to be a hurricane by then. However, if Irene follows the NHC forecast, it will have an extended encounter with Hispaniola and Cuba on Tuesday through Wednesday that will probably weaken the storm below hurricane force. Keep in mind that the average error for an official 5-day forecast from NHC for a developed storm is 200 - 250 miles. Irene could easily miss Florida and move up the East Coast and hit North or South Carolina, or pass through the Florida Keys and into Gulf of Mexico, ending up who knows where. Given the uncertainties, this weekend would be a good time to go over your hurricane preparedness if you live anywhere in the Caribbean, Bahamas, or U.S. coast, since Irene could well be paying you a visit as a tropical storm or hurricane sometime in the next week.

Harvey hits Belize
Tropical Storm Harvey made landfall at 2pm EDT on Saturday near Dangriga Town, Belize, as a tropical storm with 60 mph winds. Harvey continues to dump very heavy rains on northern Guatemala, Belize, and portions of Mexico's Yucatan Peninsula as the storm tracks westwards at 12 mph. Dissipation is expected Sunday as the storm pushes inland. Harvey was a small storm, and the strongest winds were confined to a short stretch of coast near where the center came ashore. Winds at Belize City, Belize on Saturday topped out at 15 mph.


Figure 3. Radar image of Harvey taken at 11:30am EDT on Saturday, August 20, 2011, a few hours before landfall in Belize. A small closed eye is visible just south of the offshore islands of Belize. Image credit: Belize National Meteorological Service.

An exceptionally active early part of hurricane season
It's been a strangely hyperactive season for weak storms in the Atlantic so far this year. Tropical Storm Irene is the 9th named storm this year, and its formation date of August 20 ties 2011 with 1936 as the 2nd earliest date for formation of the season's 9th storm. Only 2005 had an earlier date. The first eight storms this year have stayed below hurricane strength, making 2011 the first hurricane season since record keeping began in 1851 to have more than six consecutive tropical storms that did not reach hurricane strength. As I discussed in Friday's post, a major reason for this is the lack of vertical instability over the tropical Atlantic so far this year. We've had a large amount of dry, sinking air over the tropical Atlantic, and the usual amount of dry, dusty air from the Sahara, both helping to keep the atmosphere stable and stop this year's storms from intensifying into hurricanes. Hurricane activity typically ramps up big-time by August 20, with more than 80% of all the hurricanes and 65% of all the tropical storms occurring after that date. At our current pace, 2011 will become the second busiest Atlantic hurricane season on record, with 24 - 27 named storms. There are only 21 names in the list of names for a hurricane season, so we may have to break out the Greek alphabet again in late October this year, as occurred in 2005. Ironically, this was the last time the current set of names was used in the Atlantic, so 16 of this year's 21 names are repeats of 2005. I'm not too happy about seeing another hurricane season challenge the Hurricane Season of 2005 in any way, and let's hope we don't retire another five names this year, like occurred in 2005! With vertical instability much lower this year than in 2005, and that year having already seen one storm (Dennis) retired by this point in the season, I doubt that will happen, though.


Figure 2. The annual cycle of average hurricane frequency in the Atlantic. Historically, about 35% of all the tropical storms and 15% of all the hurricanes will have occurred by August 20.

Invest 98L near the Cape Verde Islands
A tropical wave near Cape Verde Islands off the coast of Africa, Invest 98L, is spreading heavy rains and strong gusty winds to those islands today. So far this morning, top sustained winds measured in the Cape Verde Islands were 23 mph at Mindelo. 98L has a long stretch of ocean to cross before it could affect any land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, and I'd be surprised if 98L threatens any land areas.

Jeff Masters

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Quoting MiamiHurricanes09:
11p.m track:




did the track move march of any?
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Quoting Levi32:


Just an over-adjustment. It moves WSW initially which is overdone, and then it has to overcompensate when it feels the weakness in the 500mb ridge to its north after 48 hours. A more likely track would probably be the same start and finish points, but with a more gradual curving path in between.


Please turn off and stow all electronic devices. We will tell you when it is safe to use them. These include laptops, blackberries, strawberries, anything with an off and on switch.
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I know Harvey is like... soo over... but isn't that convection over the BoC that I see????
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WATCHES AND WARNINGS
--------------------
CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY...

THE GOVERNMENT OF THE DOMINICAN REPUBLIC HAS ISSUED A TROPICAL STORM
WATCH FOR THE SOUTH COAST OF THE DOMINICAN REPUBLIC FROM THE HAITI
BORDER TO CABO ENGANO.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* PUERTO RICO...U.S. VIRGIN ISLANDS...VIEQUES AND CULEBRA
* SABA...ST. EUSTATIUS...AND ST. MAARTIN
* DOMINICA
* BARBUDA...ST. KITTS...NEVIS...ANTIGUA...ANGUILLA...MONTSERRAT
* BRITISH VIRGIN ISLANDS

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* SOUTH COAST OF THE DOMINICAN REPUBLIC FROM THE HAITI BORDER TO
CABO ENGANO

TROPICAL STORM CONDITIONS COULD OCCUR ELSEWHERE IN THE NORTHERN
LEEWARD ISLANDS TONIGHT AND EARLY SUNDAY.

HURRICANE CONDITIONS COULD OCCUR IN THE DOMINICAN REPUBLIC LATE ON
MONDAY.

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED STATES
...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE FORECAST
OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE THE
UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE.
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Quoting chevycanes:
cone will shift slightly to the west.

slightly what i was thinking :)
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Quoting MiamiHurricanes09:
11p.m track:

doesn't that say 7:00 pm on the left hand side?
PS: I do see the difference in track
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1015. GoWVU
Quoting OceanMoan:



Tree rats???


Squeirrels (spelling)
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LLego la banda... tocando salsa


Here are the first bands arriving...



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Quoting cjswilmingtoneye:
Woah buddy, easy on the caps... I think the only person stressing on this blog is you ;)


please don't feed the trolls
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1011. ncstorm
Aren't the 18Z runs useless..wont the HH data be fed into the 00z models, if so, then the new model runs just updated wont reflect the center of Irene and the true track..I will await the NHC map and see what they do..
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BULLETIN
TROPICAL STORM IRENE ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
1100 PM AST SAT AUG 20 2011

...IRENE APPROACHING THE LEEWARD ISLANDS...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...15.3N 59.9W
ABOUT 95 MI...150 KM E OF DOMINICA
ABOUT 120 MI...195 KM SE OF GUADELOUPE
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 22 MPH...35 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES
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cone will shift slightly to the west.
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Quoting Lizpr:
Just talked to my mom in Puerto Rico she didn't even know a Tropical Storm was formed and potentially hit PR.
i lot of people don't know, i hope they give good media coverage
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11p.m track:

Member Since: September 2, 2009 Posts: 130 Comments: 21122
Quoting GoWVU:
Had a nice dinner tonight in West Ashley and then friends came over and we had some cold adult beverages by the pool. One thing I have noticed is the animals are acting funny in the back yard. The tree rats in the back yard burring nuts and for the most part not seeing many... Does that mean anything?



yes...it means you've had too much beer...
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1005. Thrawst
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1004. JLPR2
Quoting Lizpr:
Just talked to my mom in Puerto Rico she didn't even know a Tropical Storm was formed and potentially hit PR.


I'm not surprised, but tomorrow the news should cover it better than today.
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Quoting 34chip:
So what is it looking like for Key West florida?
preview your hurricane plans, buy plywood just incase it get stronger. When it get stronger, people will be in long line for plywood... also get ready for evacuation when it does get closer and stronger, but we still got few more days before we find out if it's a major threat to Keys.
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Tropical Storm IRENE Storm Archive
...IRENE APPROACHING THE LEEWARD ISLANDS...
11:00 PM AST Sat Aug 20
Location: 15.3°N 59.9°W
Max sustained: 50 mph
Moving: W at 22 mph
Min pressure: 1006 mb
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1001. KEEPEROFTHEGATE (Mod)
T.C.F.W.
09L/TS/I/CX
MARK CENTRE FIX
16.63N/59.29W
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999. GoWVU
Quoting Bluestorm5:
I would preview hurricane plans and remain close eye on this storm. Too early to tell, but it a good chance it'll impact SE USA. If it get really strong in 2 or 3 days from now, get ready for the storm.


Thanks Bluestorm, I have my kit ready have not been on all day and now trying to catch up with all the latest
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Quoting Tazmanian:
what time is the next recon
Tomorrow morning Taz around 7 am EST.
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We do not tape windows waste of time.
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Quoting USAFwxguy:


Yeah I noticed that as well....kind of odd


Just an over-adjustment. It moves WSW initially which is overdone, and then it has to overcompensate when it feels the weakness in the 500mb ridge to its north after 48 hours. A more likely track would probably be the same start and finish points, but with a more gradual curving path in between.
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The new 0Z NAM for the US is out 60HRS the NE trough is moving out very fast to NE. The weakness in the ridge along the east coast will be short lived. The 0Z models are moving Irene farther west moving just south of San Juan & DR closer to Jamaica.
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TROPICAL STORM CENTER LOCATED NEAR 15.3N 59.9W AT 21/0300Z
POSITION ACCURATE WITHIN 40 NM

PRESENT MOVEMENT TOWARD THE WEST OR 280 DEGREES AT 19 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1006 MB
MAX SUSTAINED WINDS 45 KT WITH GUSTS TO 55 KT.
34 KT.......105NE 0SE 0SW 45NW.
12 FT SEAS..360NE 0SE 0SW 45NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 15.3N 59.9W AT 21/0300Z
AT 21/0000Z CENTER WAS LOCATED NEAR 15.0N 59.0W
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Quoting WeatherNerdPR:

What does TPC mean? Toilet Paper Corporation?


Tropical Prediction Center...
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Quoting kmanislander:


Yes, all out on parole LOL


Well. Haha! Isn't that special.
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Quoting Levi32:


0z NAM has it abruptly moving northward into Hispaniola.
Indeed. Helluva weakness towards the north of the cyclone.

Member Since: September 2, 2009 Posts: 130 Comments: 21122
988. Lizpr
Just talked to my mom in Puerto Rico she didn't even know a Tropical Storm was formed and potentially hit PR.
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Quoting washingtonian115:
Direct strike would be nasty.No one wants a Jeanne part 2.


Actually...Jeanne...she tracked along the N coast of the DR and I don't think the center directly hit Haiti...but a lot of sheared off moisture wound up there...so they got pummeled with Jeanne anyway....

So even if Irene in short-term tracked like Jeanne did...no guarantee for Haiti to go unscathed (although I hope they go unscathed)...although an indirect track is better than a direct strike so as to increase their chances of being okay...

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Quoting GoWVU:
Had a nice dinner tonight in West Ashley and then friends came over and we had some cold adult beverages by the pool. One thing I have noticed is the animals are acting funny in the back yard. The tree rats in the back yard burring nuts and for the most part not seeing many... Does that mean anything?



Tree rats???
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Uh oh...we got an 8 pm outlier with the GFDL.... Here we go!!!!!
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Quoting WeatherNerdPR:

What does TPC mean? Toilet Paper Corporation?
Oh wow! LOL
Member Since: August 31, 2009 Posts: 0 Comments: 5628
what time is the next recon
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Quoting NHCaddict:
Tape + Windows = Useless

Plywood + Windows = Pretty Good

Hurricane Shutters + Windows = Excellent



Cat 3 and above anywhere near me in Florida = get the hell out of Dodge.
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Quoting jonelu:
Thanks Levi...where you flying to?


I'm flying home (Homer, AK) for a few days before Fall semester begins.
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979. GoWVU
Quoting presslord:


I'll let you know when to push the panic button...


Press my wife has already started, god help me!!
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Quoting weatherwart:
Hiya Levi, Kman, Drak... all the usual suspects, I see. :)


Yes, all out on parole LOL
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i think the curent cone is perfect
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...WEAKENING HARVEY BRINGING HEAVY RAINS TO PORTIONS OF GUATEMALA AND EASTERN MEXICO...
10:00 PM CDT Sat Aug 20
Location: 17.4°N 90.2°W
Max sustained: 40 mph
Moving: W at 14 mph
Min pressure: 1003 mb
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Quoting Patrap:
Irene IR Unenhanced Image




Ugh... That's a little disconcerting Pat... Your image is the first where I'm starting to see significant banding on the South side in addition to the North.

I don't have the authority, but if I did, I'd say:

Shields Up! Yellow Alert!
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Quoting USAFwxguy:


That is a ridiculously tight cluster.
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972. wpb
who writing the 11pm advisory

blake?
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(post #804)


Yeah, and don't we know it here, too..... People are about to go nuts in the next 3 days here
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.